Purification of isocyanates

ABSTRACT

Synthetic metal silicates greatly reduce the amount of hydrolyzable chlorides and acids present in isocyanates. Isocyanates are useful, for example, in forming polyurethane materials.

United States Patent n 1 Cuscurida et al.

PURIFICATION OF ISOCYANATES Inventors: Michael Cuscurida, Austin; James Edward Kmiecik, Houston, both of Tex.

Assignee: Jefferson Chemical Company, Inc.,

Houston, Tex.

Filed: Jan. 20, 1971 Appl. No.: 108,146

US. Cl. 260/453 SP Int. Cl. C071: 119/04 Field of Search 260/453 SP References Cited UNITED STATES PATENTS 5/1958 Bloom et al. 260/453 Primary Examiner-Lewis Gotts Assistant Examiner-Dolph H. Torrence Att0rney.lohn R. Kirk, H. G. Jackson and Terrence D. Dreyer [57] ABSTRACT Synthetic metal silicates greatly reduce the amount of hydrolyzable chlorides and acids present in isocyanates. lsocyanates are useful, for example, in forming polyurethane materials.

7 Claims, No Drawings PURIFICATION OF ISOCYANATES BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to the field of isocyanate purification.

2. Description of the Prior Art Commercial isocyanates are often made by the phosgenation of amines. The crude products prepared by phosgenation contain chlorine-containing impurities which are acidic and are not efficiently removed by fractional distillation. Among these impurities are hydrolyzable chlorides and acids. I

It is to be understood that the term hydrolyzable chlorine refers to labile chlorine atoms which are loosely bound in a compound and not to a chlorine atom that is tightly chemically bound such as chlorine is in chlorobenzene. This value may be determined by extracting the chlorine from the isocyanate by hot solution in an aqueous-methanol solvent, or liberating the chlorine on hydrolysis of the compound with water. The extract is then subjected to a potentiometric titration of the chloride ion concentration with a standard silver nitrate solution. From the amount of silver nitrate necessary, the percentage of the hydrolyzable chlorine can be determined by a simple calculation. The term acidity as understood here is determined essentially in the same manner as the hydrolyzable chlorine content except dilute caustic is used in the titration of the free I-lCl or acid. From the amount of caustic used, the percent acidity as HCI can be determined.

The hydrolyzable chlorine and acidity have been reduced in the past by fractional distillation, but such a process is inconvenient, costly and inoperable for use when the particular isocyanate has a boiling point similar to the hydrolyzable chlorine containing material. Also, a high boiling isocyanate is difficult to distill under fractionation without high yield losses due to prolonged overheating.

Also, the hydrolyzable chlorides and acids may be reduced by the addition of metallic salts of iron. This method has serious drawbacks, however, since a considerable portion of the treating agent dissolves in the isocyanate thereby contaminating it.

-The use of synthetic metallic silicates, however, solves these problems since treatment with insoluble silicates introduces only very small amounts of metal into the isocyanate and the spent treating agent may be recovered by simple filtration.

It is even possible using the process of my invention to reduce the hydrolyzable chloride and acid content of commercially available isocyanates which have presumably already been treated in some way to reduce these contaminants.

SUMMARY OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of our invention may be carried out by contacting polymeric isocyanates with synthetic metal silicates for a sufficient length of time to reduce the hydrolyzable chlorides and acid to a desired level.

Synthetic metal silicates are useful in the process of our'invention. For example, those resulting from the fusion of metal carbonates with silica at high temperatures. In this process carbon dioxide is driven off and a complex mixture of metal silicates is obtained. Other methods of preparing synthetic metal silicates are old in the art and are explained in standard encyclopedias and textbooks dealing with the subject. For example, see Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Edition, lnterscience, New York, 1969, 18, p. 157-159 and Cotton, G. W. and Wilkinson, F. Albert, Advanced Inorganic Chemistry, lnterscience, 1962, p. 357.

Various synthetic metal silicates made in this manner are useful in the process of our invention. For example, the silicates of magnesium, calcium, zinc, lithium, barium, and aluminum are useful.

The synthetic metal silicates should be brought into intimate contact with the isocyanate to be treated. Of course the more finely divided the synthetic silicate is the shorter the contact time required to reduce the contaminates to a desired level. The examples which follow illustrate typical contact times and corresponding reductions in contaminates.

The isocyanates to be treated may be completely untreated or they may be commercial products. In either case the process of our invention is useful for reducing the hydrolyzable chloride and acid content.

The following examples will illustrate the process of our invention but are not to be construed as limiting its scope.

EXAMPLE 1' Analyses of the isocyanate before and after treatment were as follows:

Before After Treatment Treatment Sodium (ppm.) Unknown 0.7

Magnesium (ppm.) Unknown 08 Total Chloride (wt. 0.59 0.39

Hydrolyzable chloride (wt. 0.20 0.03

Total acidity (wt. as HCl 0.17 0.02

Thus, most of the hydrolyzable chloride and acidity were removed from the isocyanate and very little magnesium was introduced.

EXAMPLE 2 Using the same equipment, the same amounts of isocyanate and synthetic magnesium silicate and operating in the same manner as described in Example 1 except at 4559 for 2 hours, the following results were obtained:

After Before Treatment Treatment Sodium (ppm.) Unknown 0.1 Magnesium (ppm.) Unknown 0.5 Total chloride (wt. 0.59 0.4\

Total acidity (wt. as HCl) From these results it is apparent that treatment at about 50 removes chlorides and acidity from isocya- EXAMPLE 6 nates, although not as effectively as treatment at 100 (Example This example illustrates the increase in iron content observed in a nondistillable isocyanate when ferric EXAMPLE 3 chloride of the prior art is used as a treating agent in an This exampe shows that isocyanates can be treated attempt to lower hydrolyzable chloride and acidity levwith synthetic magnesium silicate at elevated tempera- 10 tures with no significant increase in viscosity or change A 500 e 'PP as desetlbed th Example 1 in isocyanate content. was charged with 250 g. of polymethylene polyphenyl A 500 mL fl k equipped as described in Example 1 isocyanate and 0.25 g. of anhydrous ferric chloride.

0 was charged with 250 g. of 2.2 functional polymethyl- The mlxthl'e was uhdet hlttogeh at for 2 ene polyphenyl isocyanate and 10 g. f dry Synthetic hours and filtered. The recovered ferric chloride was magnesium silicate. The mixture was stirred under ninot Weighed but pp e to be approximately the trogen at 125 for 2 hours, cooled slightly and filtered amount added at the heglhhthg of the P to remove the treatment ag nt, Anal f th i Analyses of the isocyanate before and after treatment nate before and after treatment were as follows: ere

Before After B f M. Treatment Treatment e ore Total chloride wt. 0.59 0.41 T'eatmem Treatment Hydrolyzable chloride (wt. 0.16 0.05 chlmlde 1 Total acidity (wt. as HCl) 0.12 0.03 y mple chloride (wt. 0.20 0.16 viscosity (CPSJ 75 [00 Total acidity (wt. as HCl) 0.17 0.13 isocyanate equivalent weight 133 134 content PP 257 EXAMPLE 4 Thus, while a slight reduction in chloride and acid A qi fla k i d as d ib d i E l 1 content occurs, the iron content rises to an undesirable was charged with of functional p lymethyL value. The ll'Ol'l COUlCl be removed by distillation of a @ne l h l isocyanate d 40 f d h ti lower boiling isocyanate such as toluene diisocyanate. magnesium silicate. The mixture was stirred under ni- Since polymethylene polyphenyl isocyanate cannot be trogen at 125 for 2 hours and the magnesium ilicate distilled, ferric chloride cannot be used as a treating was removed by filtration. Analyses of the isocyanate agent. before and after treatment were as follows:

EXAMPLE 7 Before After Treatment Treatment This example illustrates the use of synthetic silicates mz ffigg g gghgg gig 8:3; other than magnesium silicate in the removal of hydro- Total acidity (wt.% asHCl) 0.17 0.03 lyzable chlorides and acidity from isocyanates. in all EXAMPLE 7 Total chloride Hydrolyzable chloride Total acidity (wt. percent) (wt. percent) (wt. percent at lICll Amount of isocyanate Amount of Treatment 'lempera- Before After Before After Before After Silicate used (g.) silicate (g.) time (11rs.) ture 0.) treatment treatment treatment treatment treatment treatment Aluminum 250 10 2 125 0. .10 0. 0. 20 0.11 0.17 0. 011 liurium 250 10 2 125 0. 50 0. 5s 0. 20 0. 0t 0. 17 0. 01 Lithium 250 10 2 125 0. 50 0. 40 0. 20 0. 10 0. 1r 0. us Zinc 250 25 z. 00-110 0.111 0. 4s 0. 10 0. 02s 0. 16 N11 Magnesium 250 10 2 125 0. 0. 41 0. 20 0. 05 0. 17 0. 03 Calcium 250 10 2 125 0. 01 0. 32 0. 18 0. 03 0. 12 0. 01

Thus, magnesium Silicate treatment of a fUnC- 5 instances the silicate was stirred with the polymethyltional polymethylene polyphenyl isocyanate effectively removes hydrolyzable chloride and acidity.

EXAMPLE 5 respectively.

Treated lsocyanate Total Total Hydrolyzable acidity Silicatezisocyanate chloride chloride (wt. weight ratio (wt. (wt. as HCl ene polyphenyl isocyanate under nitrogen.

EXAMPLE 8 This example illustrates the improvement in rigid foam cell structure obtained by treating a polymethylene polyphenyl isocyanate with synthetic magnesium silicate. Treatment of the isocyanate using the general process described in previous examples reduced hydrolyzable chloride and acidity from 0.10 wt. percent and 0.08 wt. percent (as HCl) to 0.02 wt. percent and 0.008 wt. percent (as HCl).

Using a typical rigid urethane polyol rigid foams were prepared using treated and untreated isocyanate. The cell structure of the foam from untreated isocyanate was very coarse and open, containing only 0.03 percent closed cells. In contrast, foam prepared using the same formulation with treated isocyanate, appeared normal and had 88 percent closed cells.

EXAMPLE 9 This example illustrates general improvements in foam qualities that can be obtained by treating the isocyanate component with synthetic magnesium silicate. Two 2.2 functional polymethylene polyphenyl isocyanates (designated A and B) were treated following the general procedure given in previous examples. Using a standard formulation, rigid foams were then prepared from treated and untreated isocyanates and the same polyol used in Example 8. Analyses of the isocyanates before and after treatment as well as qualities of foams prepared from them are given in the following table.

and the resulting superior yields obtained.

We claim 1. In a process to remove hydrolyzable chloride and Isoeyanate Untreated Treated Untreated Treated Total chloride (wt. percent) 0.87 0. 49 0.82 0. 50 Hydrolyzable chloride (wt. percent) 0.28 0. 06 0.31 0. 08 Total acidity (wt. percent as HCI) 0.21 0.04 0. 22 0.05 Foam properties:

Cream time (sec.) 45 45 45 45 Rise time (sec.). 240 240 230 210 Tack-free time (see. 210 160 180 165 Density (lo/1L 1. 7 1.8 1. 7 1. 8 K-faetor 0. 172 0. 130 O. 153 0. 126 Compress. strength, W.R 28. 7 33. 6 28. 3 33. 9 Percent closed cells. 76. 4 90. 0 81. 7 90. 0 Burn rate (in/see.) 1. 76/32. 8 1. 52/33. 2 1. 60/32 1. 38/31. 4

The beneficial effects of synthetic magnesium silicate treatment of isocyanates are observed from a study of the two sets of data tabulated above.

EXAMPLE 10 This example illustrates the improvement in hydrolyzable chloride and acid content of commercial isocyanates using synthetic magnesium silicate. Significant improvements were noted in all cases. A'foam was made in each case using identical formulations to show that reaction rates were increased without degradation of physical properties of the foam.

acid contaminates from isocyanates the improvement which comprises contacting the isocyanate with synthetic metal silicates wherein the synthetic metal silicate is the silicate of magnesium, calcium, zinc, lithium, barium or aluminum. 2. The process of claim 1 wherein the synthetic metal silicate is the silicate of magnesium.

3. The process. of claim 1 wherein the synthetic metal silicate is the silicate of calcium.

4. The process of claim 1 wherein the synthetic metal silicate is the silicate of zinc.

EXAMPLE 10 A B C D E Isocyanatc Untreated Treated Untreated Treated Untreated Treated Untreated Treated Untreated Treated Isocyanatc equivalent. 132. 5 140.0 132. 1 135. 7 134.4 141. 2 133. 3 135.0 135. 4 136.1 Total chloride, Wt. peree 0 53 0. 41 0. 0. 19 0. 73 0. ti] 0. 44 O. 0. 41 0. 30 Hydrolyzable chloride, wt. 0 0. 12 0.13 0.04 0.33 0. 16 0. 18 0. 12 0. 12 0. 12 Acidity, wt. percent as 1101 0. 10 0. 01 0.02 0. 004 0. 18 0. 04 0.07 0. 0.2 0. 10 0.02 Wt. percent MDI 51-0 49. 2 49. 6 48. 8 49.1 51. 4 45 7 50.1 68. 2 72. 0 Isomer distribution in MDI:

Wt. percent 2,2 3. 9 4.3 0.1 0.1 0.1

Wt. percent 2,4 31. 6 30. 8 4. 3 4. 4 1. 2 0. (i 2. 7 3. El 1. 0 I. 4

Wt. percent 4,4 64. 5 64. 9 95. 7 95. 6 98. 8 9!). 4 97. 3 U6. 0 )9. 0 118. 6 Reaction rate (foam):

Cream time, sec 50 50 47 50 45 43 45 45 43 Rise time, Sec 250 225 240 235 230 215 105 240 210 Tack free time, Sec 190 165 160 160 175 135 145 Physical properties (foam):

Density, p 1 114 1.92 1. 97 l. 94 1.110 1, 116 1. 94 1. E14 1.80 1, S!

K-factor 0 1 3 0 121 0.127 0.123 0.12 0.122 0.126 0.133 0. 134 0. 128

Compr. strength, W.R. 30 40 36 40 38 40 37 37 33 35 Heat dist. temp., C 164 167 171 172 171 169 178 166 162 Percent closed cells. 92 90 )1 u! 92 12 1 0 '1 Burn, in./see 1. /32 1. 4/35 1. 4/32 1. 3/31 1. 0/35 1.1/35 1. 5/33 1.5/33 1 6/35 1 4 Volume change. percent Dimensional stability:

1 wk., -20 F., dry 3.0 2.5 -3.0 -3 2 -s 7 -3 5 -3.4 -3.2 -3.2 2. 7

1Wk.,180 F.,dry 2.2 2.2 2.6 2.4 2.4 2.4 2.7 2.4 2.2 2.6

1 Wk., 158 F., 100% R. 6.1 7. 8 5.3 5.5 T. 1 -1. 8 5.1 4. 4 6. 2 5.1

It is to be understood that the synthesis of the organic isocyanate does not form a part of this invention. The product from any method of preparing organic isocyanates which results in the final product having a hydrolyzable chlorine or acidity content may be treated by the process of this invention to remove the hydrolyzable chlorine containing substituents. As an example of 5. The process of claim 1 wherein the synthetic metal silicate is the silicate of lithium.

'6. The process of claim 1 wherein the synthetic metal 65 silicate is the silicate of barium.

7. The process of claim 1 wherein the synthetic metal silicate is the silicate of aluminum. 

2. The process of claim 1 wherein the synthetic metal silicate is the silicate of magnesium.
 3. The process of claim 1 wherein the synthetic metal silicate is the silicate of calcium.
 4. The process of claim 1 wherein the synthetic metal silicate is the silicate of zinc.
 5. The process of claim 1 wherein the synthetic metal silicate is the silicate of lithium.
 6. The process of claim 1 wherein the synthetic metal silicate is the silicate of barium.
 7. The process of claim 1 wherein the synthetic metal silicate is the silicate of aluminum. 